1. Field of the Invention
The present invention relates to an electron gun in a cathode ray tube (CRT), and more particularly, to an electron gun in a CRT, in which electron beam pass through holes in an electrostatic field controlling body provided both to a focusing electrode and anode of a main lens electrode are changed, for improving a screen focusing characteristic.
2. Background of the Related Art
The CRT, a device for forming a picture by landing electron beams emitted from the electron gun on a screen, is illustrated in FIG. 1, schematically.
Referring to FIG. 1, the CRT is provided with a panel 2 fitted to a front for acting as a screen, a fluorescent surface 4 of red R, green G, and blue B fluorescent materials coated on an inside surface of the panel 2, a shadow mask 8 for selecting a color as electron beams 6 incident on the fluorescent surface 4 pass therethrough, a funnel 10 fitted to rear of the panel 2 for sustaining an inner space of the CRT at a vacuum, and a deflection yoke 12 surrounding an outer circumference of a neck part 10a of the funnel 10 for deflecting the electron beams 6.
The electron gun 20 is placed in the neck part 10a of the funnel 10 of the CRT, and provided with three independent cathodes 201, a first electrode 21 spaced a distance away from the cathodes 201, a second electrode 22, a third electrode 23, a fourth electrode 24, a fifth electrode 25, and a sixth electrode 26 spaced at fixed intervals from the first electrode 21, and a shield cup 27 above the sixth electrode 26 having a bulb space contact (B.S.C) 28 fitted thereto for electrical connection of the electron gun 20 to the funnel 10 and fastening the electron gun 20 to the neck part 10a of the funnel 10.
The electron gun 20 emits electrons as heaters 203 in the cathodes 201 are heated by a power supplied from respective stem pins 202 at rear end thereof, and the electrons form electron beams, which are controlled by the first electrode 21, a controlling electrode, and accelerated by the second electrode 22, an accelerating electrode. Then, the electron beams are partly focused and accelerated by a pre-focus lens formed between the second electrode 22, the third electrode 23, the fourth electrode 24, the fifth electrode 25 (a focus electrode), finally focused and accelerated by the sixth electrode 26 (anode), a final accelerating electrode, pass through the shadow mask 8, and land on the fluorescent surface 4 on an inside surface of the panel 2, to make the fluorescent surface to emit a light.
The focus electrode 25 and the anode 26 collectively called as a main lens 200, and a related art main lens 200 will be explained with reference to FIG. 2. FIG. 2 illustrates a perspective view with a partial cut away view of the focus electrode 25 and the anode 26 in the main lens electrode.
Referring to FIG. 2, the focus electrode 25 is provided with a drum formed housing 252 externally, having an fore end facing the anode 26 with an opened central part and a rim 252a in a form of a racing track in a periphery, and a plate of electrostatic field controlling body 254 spaced a distance away inward from rim 252a with three electron beam pass through holes 254a, 254b, and 254c for passing the three electron beams from the cathodes. The anode 26 is also provided with a drum formed housing 262 having a rim 262a at one end, and an electrostatic field controlling body 264 with electron beam pass through holes 264a, 264b, and 264c inside thereof.
FIGS. 3a and 3b illustrate a plan view of the electrostatic field controlling bodies 254 and 264 of the focus electrode 25 and the anode 26, respectively.
Referring to FIGS. 3a and 3b, it can be known that the electron beam pass through holes 254a, 254b, and 254c in the electrostatic field controlling body 254 of the focus electrode 25 are similar, or identical to the electron beam pass through holes 264a, 264b, and 264c, respectively.
One of the most important parameter to be taken into account in design of an electron gun is a spot diameter Dt on a screen. There are three factors that influence the spot diameter on the screen, i.e., a magnification of the lens, a spatial charge repulsive power, and a spherical aberration of the main lens. Since voltage conditions, focal distances, a length of the electron gun, and etc., are already defined basically, the influence of the magnification of the lens to the spot diameter Dx has a small portion for utilizing as design parameter of the electron gun, and minimal effect.
The spatial charge repulsive power is a phenomenon in which the collision and repulsion between the electrons in the electron beam enlarge the spot diameter. For reducing enlargement of the spot diameter Dst caused by the spatial charge repulsive power, it is favorable to design an angle (a diverging angle) of the electron beam travel greater.
The spherical aberration of the main lens can form the smaller spot diameter on the screen, as the diverging angle of the electron beams is the smaller. In general, the spot diameter Dt on the screen may be expressed as a sum of three factors as follows.
Dt={square root over ((Dx+Dst)2+Dic2)}
The best method for reducing the spherical aberration as well as the spatial charge repulsive power is enlargement of the main lens diameter, which reduces enlargement of the spot caused by the spherical aberration even if electron beams with a great diverging angle are incident thereon, and reduces the spatial charge repulsive power after electron beams pass through the main lens, thereby forming a small diametered spot on the screen. However, an enlargement of the rim, and spacing the distance from the rim to the electrostatic field controlling body greater for enlargement of the main lens diameter form the spot to be almost triangular with partial halo as a focusing of the outer main lens is in a 45xc2x0 direction, with a difference between a central main lens side and an opposite side.
FIG. 4 illustrates the foregoing triangular spots S1 on the screen.
The rim 252a of the focus electrode 25 focuses the outer beam weak in a 45xc2x0 direction on the central beam side, and strong in a 45xc2x0 direction on an opposite side of the central beam side, to form a triangle greater vertically in the 45xc2x0 direction on the central beam side, and smaller vertically in the 45xc2x0 direction on an opposite side of the central beam side. There are halos on sides opposite to the central beam in 45xc2x0 directions. Of course, though forms of the outer spots can be slightly corrected at the anode as the anode acts opposite to the focus electrode, since an action of the main lens is significantly greater at the focusing side than the acceleration side, eventually a state at the focusing side is maintained as it is, due to which, because spot is formed not circular at a periphery of a picture, realization of focusing for meeting requirements of high definition, large sized screen, flat screen, and wide angle is difficult.
Moreover, in comparison to the electron gun with circular outer spots, alignments between apertures of electrodes of electron gun and one sided halo inducing characteristic dependent on assembly of electron gun related to a flatness of the electrode are sensitive, assembly of the electron gun is unfavorable.
Accordingly, the present invention is directed to an electron gun in a CRT that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an electron gun in a CRT, which can enlarge a main lens diameter and form an excellent spot that is almost circular and has a reduced size.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the electron gun in a CRT includes a main lens electrode having a focus electrode and an anode for focusing electron beams emitted from cathodes onto a screen, an electrostatic field controlling body fitted in each of the focus electrode and the anode each having three electron beam pass through holes, wherein each of outer holes in the electrostatic field controlling body fitted to each of the focus electrode and the anode has a form of a combination of a circle and a rectangle with reference to a vertical axis through a center of the hole in a direction opposite for facing outer holes of the focus electrode and the anode.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.